Bronchial asthma categorized clinically into various subsets of disease, will be studied in spontaneous and in induced asthmatic attacks with respect to: 1) their pulmonary mechanics, including ventilation/perfusion ratios (VA/Q) by which two populations of gas exchange units are identified; and 2) detectable changes in their plasma histamine, serum complement, and serotonin levels. Special attention will be given to the aspirin-sensitive asthmatics, as an important subset. Further studies of complement, histamine and serotonin will be carried out in chronic urticaria and in patients with reactions to radiographic contrast materials. Metabolic turnover studies of serum complement components will supplement observed abnormalities in component titers. These studies are expected to provide new insights into mediators of these two types of vascular disorder.